Inert gases, such as argon, are used in many chemical and electronic component manufacturing processes to provide an inert atmosphere for carrying out these processes. For example, in the production of ultra high purity silicon crystals it is necessary that certain operations of the crystal manufacturing process be carried out in a completely inert atmosphere. Because of their substantially nonreactive nature, noble gases are the most suitable gases for such processes. Since argon is the most abundant and least inexpensive of the noble gases, it is usually preferred for use as the inert gas in these processes. However, the relatively high cost of argon makes it generally necessary to recover and reuse the argon. Unfortunately, certain operations in the manufacturing process, particularly in the argon recovery procedure, for example vacuum evacuation of manufacturing chambers, result in the infiltration of atmospheric impurities into the argon. These impurities and the impurities produced during the processes must be removed before the argon can be reused in the manufacturing operations.
Various techniques have been employed in the purification of argon. For example, U.S. Pat. No. 5,106,399, teaches a multiple step process for removing one or more of oxygen, nitrogen, water vapor, hydrogen, carbon monoxide, carbon doixide and hydrocarbon impurities from an argon feed stream. According to the process disclosed in this patent, water vapor and/or carbon dioxide are removed from the feed stream at ambient temperature by adsorption, oxygen, hydrogen and/or carbon monoxide are then removed by ambient temperature chemisorption using a catalytic material, and nitrogen and/or hydrocarbon are removed from the gas stream by absorption at cryogenic temperatures. A disadvantage of the process disclosed in this patent is that, if there are more than trace concentrations of oxygen, hydrogen and carbon monoxide in the feed stream, a large bed of catalytic material must be used for the chemisorption of these gases.
Japanese Patent Documents JP62119104 JP94024962 disclose the removal of oxygen from an argon gas stream by first adding hydrogen to the gas stream, then catalytically reacting the oxygen and hydrogen to form water, then contacting the gas stream with a copper oxide catalyst to convert carbon monoxide and excess hydrogen to carbon dioxide and water, respectively, and then removing water, carbon dioxide and nitrogen from the gas stream by pressure swing adsorption. This leads to low recovery of the argon.
Japanese patent document JP 89-102315 discloses the removal of carbon monoxide from an argon gas stream by catalytically oxidizing the carbon monoxide with oxygen, removing oxygen from the gas stream by reacting it with hydrogen, removing the resulting carbon dioxide and water vapor from the gas stream by adsorption and further purifying the argon by cryogenic fractional distillation.
U.S. Pat. Nos. 5,110,569 and 5,202,096, issued to Jain, disclose purifying an air stream containing carbon monoxide, hydrogen, carbon dioxide and water vapor by removing water vapor from the gas stream by adsorption, then oxidizing the carbon monoxide to carbon dioxide with oxygen in the presence of a metal oxide catalyst, then oxidizing the hydrogen to water vapor with oxygen in the presence of a noble metal catalyst, and finally, removing the resulting carbon dioxide and water vapor from the gas stream by adsorption. The disclosures of these patents are incorporated herein by reference and made a part of this specification.
Japanese patent disclosure Kokai 256418/92 discloses a catalytic procedure for removing carbon monoxide, hydrogen, carbon dioxide, water vapor and oxygen from an inert gas stream. The disclosure of this patent is incorporated herein by reference.
U.S. Pat. Nos. 4,239,509 and 5,159,816 disclose the separation of nitrogen and oxygen from an argon gas stream by cryogenic adsorption comprising passing the gas stream through nitrogen-selective adsorbent, such as zeolite 5A, and then passing the gas stream through an oxygen-selective adsorbent, such as zeolite 4A.